Various devices such as barcode scanners, compact disk players, DVD players, and others use light to perform various functions, such as read data from or write data to optical media. Beams of light are also used in communication devices, sample analyzing devices, distance measurement devices, and time measurement devices.
Light can be controlled using standard lenses and mirrors. These passive methods can be made active via mechanical motion. For example, mirrors can be placed on galvo-motors to move the mirror to control the direction of light propagation. This technique is used in barcode scanners, or optical read/write heads in CD/DVD players. However, mechanical control over light is problematic for several reasons, as recognized by the present inventors. First, it is difficult to make such mechanical devices compact. Second, the mechanical nature of such moving devices have limited lifetimes due to mechanical wear and failure issues. Third, mechanical devices are inherently vibration sensitive, which limits the type of environment in which they can be used. Finally, mechanical devices necessitate a level of design complexity including gears, bearings, and other mechanical components which add cost, expense, and maintenance issues to such designs.
Rather than move a lens or a mirror with a motor or actuator, light can be controlled through the use of waveguides. For instance, U.S. Pat. No. 5,347,377 entitled “Planar Waveguide Liquid Crystal Variable Retarder” relates generally to providing an improved waveguide liquid crystal optical device, and discloses in Table I the use of alternating current voltages between 2 and 50 volts rms for retardation of the polarized light by controlling only the optical phase delay.
With conventional waveguides, electro-optic materials such as lithium niobate are generally employed in the core whereby a voltage applied across the core material changes the index of refraction, n. However, with conventional techniques using materials such as lithium niobate, the index of refraction can only be changed a very small amount so that the retardation of a half wave may require thousands of volts. This limitation makes this type of light control extremely limited, and to date not a viable alternative to mechanical control of light.
In non-waveguide devices, liquid crystal materials have become widespread in display applications where light is attenuated but not steered nor refocused. However, in order to use conventional display techniques for liquid crystal materials to attempt continuous steering of light, prohibitively thick layers of liquid crystal materials (greater than 100 microns) would be needed, which would render the device highly opaque and slow. The thick layers of liquid crystal can take seconds or even minutes to change, and can be difficult to control. Although non-waveguide, electro-optic beam-steerers have been made with standard thin liquid crystal cells, such devices have only realized minimal steering, in the range of 10−6 degrees of steering).
U.S. Pat. No. 3,963,310 entitled “Liquid Crystal Waveguide” teaches of utilizing liquid crystal—within the core of a waveguide. However, as recognized by the present inventors, such a waveguide would be problematic in that there would be substantial losses or attenuation of light traveling through such a waveguide.
Accordingly, as recognized by the present inventors, what is needed is a liquid crystal waveguide for controlling light that permits active control of the propagation or refraction of light through the waveguide in a manner that provides for low loss operation.
It is against this background that various embodiments of the present invention were developed.